1. Field of the Invention
This invention relates to a cylindrical can body formed by ironing the side wall of a cup which has been produced by drawing a metal disc (hereinafter called a D&I can body) and also relates to a filled D&I can, filled with beverage under pressure and generating or exerting positive internal pressure in the can (hereinafter called internal pressure), for example, beer, carbonated beverages, etc., such can body being seamed with a metallic top closure (hereinafter called a D&I can).
2. Description of the Prior Art
A top closure of a conventional D&I can now available on the market has, in sequence from the outermost edge of said closure as shown in FIG. 1, a seamed portion 31, a countersunk portion 32 which extends almost parallel to the side wall of the can body, a bead portion 33 which continues from said countersunk portion 32 (portion 31, 32 and 33 constituting an outer peripheral portion 39 of the top closure), a central portion 34 of the top closure which extends from and is surrounded by said bead portion 33 beyond a small curved portion 37, said central portion 34 being slightly domed upwardly and staying inside of the can end plane 40 (the meaning of can end plane is defined hereinafter) and a ready tearing and opening tab 36 fixed to the center of said central portion 34 with a rivet 35 (normally termed an easy opening top closure), and the D&I can body of said D&I can has a bottom 2 which comprises an outer peripheral portion 5 having a semi-circular inwardly turning portion 3 which turns upwardly from the lower end of the straight side wall 1, an inclined wall 4 which extends upwardly from said turning portion 3, and a high domed central portion 6 which is an extension of and is surrounded by said inclined wall and which in whole stays inside of the can end plane 7.
When such shape of the bottom of this D&I can body is used for a beer can, for example, it does not suddenly distend into an outwardly projecting shape (namely, does not buckle) at the inwardly turning portion 3 and inclined wall 4 under the internal pressure exerted within same by the pressure produced in the beer-filled bottle during the pasteurizing process, while the domed central portion 6 of said bottom is most resistant to deformation by the internal pressure because it is structural-dynamically provided with such buckling resistant strength as prevents deformation of the entire bottom wall (the buckling resistant strength of the top closure and the bottom with such profile as aforementioned being obtainable by using adequate dimensions and wall thickness of said bottom) until it buckles.
The other type of bottom of conventional D&I can bodies comprises, as illustrated in FIG. 9, a turning portion 73 which turns sharply at the lower end of the straight side wall 71 of said D&I can body, inclined wall 74 which connects to said turning portion 73 and extends upwardly (73 and 74 constituting a bottom peripheral portion 77), a second turning portion 79 which turns sharply at the upper end 78 of said inclined wall 74, inclined inner wall 76 which is an extension of said second turning portion 79 and extends downwardly, and a flat portion 75 which is connected to said inclined inner wall 76 and stays inside of the can end plane 81 (75 and 76 constitute a dish-shaped central portion 80), and is provided with buckling resistant strength which is the same as that of the bottom of the can illustrated in FIG. 1 which prevents deformation when subjected to the internal pressure, said buckling resistant strength of the bottom with aforementioned profile being achieved by using adequate dimensions and wall thickness of said bottom.
Conventional beer-filled D&I cans having the bottom illustrated in FIG. 9 and a diameter of approximately 65 mm comprises a D&I can body made of 0.40mm thick aluminum alloy sheet and an easy opening top closure seamed thereto.
The bottom and top closure of any one of the conventional D&I cans illustrated in FIGS. 1 and 9 are provided with such buckling resistant strength as withstands the maximum allowable pressure for a bottle which is the average pressure calculated by measuring the positive internal pressure in a plural number of bottles filled with pressurized beverage such as beer and heated to the specified maximum temperature, plus a safety pressure value, and thus do not buckle, and in particular, the bottom is so constructed as to undergo little if any deformation. However, it has been observed that the top closure of the conventional D&I can distend outwardly when an internal pressure is generated therein, which results in increasing the volume of the can and consequently presumably makes the internal pressure lower than that in a bottle. If so, a D&I can need only be provided with such buckling resistant strength as withstands that reduced internal pressure, but no conventional D&I can has ever adopted such concept and the bottom wall and the top closure wall are actually made thicker and stronger than necessary.
Considering the fact that an enormous number of D&I cans for pressurized beverages are consumed per year and the consumption is increasing year by year, even a slight reduction of the amount of material used per can would greatly contribute to conservation of resources including raw and finished materials and the energy employed for producing the same. A D&I can body of reduced weight is disclosed in the U.S. Pat. No. 3,904,069. This D&I can body, as shown in FIG. 2, comprises a side wall 11, a flat annular panel portion 13 which intersects said side wall 11 at right angles and forms the outer peripheral portion of the bottom portion 12 and a domed central portion 14 which is surrounded by said flat annular panel portion 13, and is provided with such buckling resistant strength as substantially inhibits the domed central portion 14 from distending outwardly while and when the flat annular panel portion 13 deforms into a conical shape as shown in FIG. 3 when subjected to an internal pressure of up to 6.3kg/cm.sup.2 (90 p.s.i.) for beer and 6.7kg/cm.sup.2 (95 p.s.i.) for pressurized gas-containing beverage, said buckling resistant strength being obtainable by using adequate dimensions and thickness of the bottom wall. This can body has an advantage that the amount of material required for a unit of this can body is less than that for said conventional D&I can body, which means that a can body with the same volume at that of a coventional D&I can body can be obtained using a smaller quantity of material, because the domed central portion of the bottom wall of this can body is made smaller than that of said conventional D&I can body so as to allow such a distension of the bottom as shown in FIG. 3, which enables this can body to keep the internal volume the same as that of a conventional D&I can body with smaller area of overall can body and also enables the bottom wall to be made thinner than that of conventional D&I can body while keeping the same buckling resistant strength, and it is estimated that approximately 15% reduction in the weight of the can body was realized. No particular form of top closure is disclosed as being used for the D&I can body in the specification of this U.S. Patent. However, the can body of this patent can keep upright standing only in a comparatively unstable condition since the flat annular panel portion 13, once deformed into the conical shape as described above, generally maintains its shape even at normal temperature ("normal temperature" being defined hereinafter) without restoring its original shape (FIG. 2) with the result that when placed in an upright position on the table or the like, it sits on the bottom ridge 17 of the cone shape which is smaller in diameter than that of the outer peripheral portion of the bottom shown in FIGS. 1 and 9. Furthermore, the bottom wall of the D&I can body covered by this U.S. Patent still has a buckling resistant strength as in the case of the D&I can bodies in FIGS. 1 and 9 which withstands the maximum pressure in a bottle described hereinbefore, which magnitude of buckling resistant strength is not required principally because no attention is given to the increased internal volume caused by the distension of the bottom and the consequent reduction in the internal pressure. This means that the bottom wall thickness is still greater than necessary.